An existing Long Term Evolution (LTE) system includes two frame structures: a frame structure type 1 that is applied to frequency division duplex (FDD), as shown in FIG. 1, and a frame structure type 2 that is applied to time division duplex (TDD), as shown in FIG. 2. For the TDD, the existing system includes seven uplink-downlink configurations.
In an LTE system, to support hybrid automatic retransmission, user equipment needs to feed back, to a base station by using a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH), a hybrid automatic repeat request-acknowledgement (HARQ-ACK) of physical downlink shared channel (PDSCH) transmission. The hybrid automatic repeat request-acknowledgement may be briefly referred to as an acknowledgement (ACK)/a negative acknowledgement (NACK). The user equipment needs to receive, by using a physical hybrid automatic repeat request indicator channel (PHICH), a hybrid automatic repeat request-acknowledgement HARQ-ACK corresponding to the physical uplink shared channel.
In the existing system, for the FDD, an HARQ-ACK corresponding to a PDSCH transmitted in a downlink subframe n−4 is fed back in an uplink subframe n. For the TDD, an HARQ-ACK corresponding to a PDSCH transmitted in a subframe n−k is fed back in an uplink subframe n, where k belongs to a set K. A definition of K for each TDD uplink-downlink configuration is shown in Table 1. For example, for a TDD uplink-downlink configuration 1, a subframe 7 is an uplink subframe and a corresponding set K is {7, 6}. A subframe 1 is reached after the subframe 7 is shifted forward by six subframes, and a subframe 0 is reached after the subframe 7 is shifted forward by seven subframes. Therefore, an HARQ-ACK corresponding to PDSCHs transmitted in the subframe 0 and the subframe 1 is fed back in the subframe 7.
TABLE 1Downlink association set K for a TDD systemUplink-downlinkSubframe nconfiguration01234567890646417, 647, 6 428, 7, 4, 68, 7, 4, 6 37, 6, 116, 5 5, 4412, 8, 7, 116, 5, 4, 7 513, 12, 9, 8, 7, 5, 4, 11, 6677577
It can be learned from Table 1 that the existing TDD system has different HARQ-ACK timing for different uplink-downlink configurations, and has higher complexity compared with an FDD system.